Since, diamonds have inherent characteristics as high hardness, high thermal conductivity, high thermal resistance, and excellent chemical stability;
diamonds have been utilized for many applications, such as, abrasion resistance materials, electronic device/sensor materials, biotechnological materials, and optical materials. Widely applied methods to produce diamonds are; the vapor-phase synthesis method using various kinds of CVD processes, and/or a synthesis method using an ultrahigh pressure/high temperature (HP/HT) apparatus.
It is well known that diamonds are inherently non-conductive material. However, in recent years, the boron-doped diamond has attracted notice due to its semiconductor characteristics. The following are known examples of producing the boron-doped diamond; the vapor-phase synthesis method in which a small amount of boron components are added to a reaction gas while synthesizing the diamond; and the HP/HT synthesis method in which under the conditions of a pressure in the range of 5 to 10 GPa and a temperature in the range of 1300 to 2000° C., the diamond is synthesized from graphite powder and boron powder as the material powders.
Also, since diamonds inherently have characteristics such as hardness and abrasion resistance, thus diamond sintered compacts are used in various cutting tools. Such diamond sintered compacts are generally produced by sintering under HP/HT conditions. The following are known examples of producing the diamond sintered compact: a method in which the diamond-Co (cobalt) based sintered compact is produced from diamond powder and Co powder as material powders; the material powders are sintered in the HP/HT apparatus under the conditions of a pressure of about 5.5 GPa and a temperature of about 1500° C. Another method in which the diamond-ceramics based sintered compact is produced from diamond powder, Ti (titanium) powder, Zr (zirconium) powder and Cr (chromium) powder as material powders; the material powders are sintered in the HP/HT apparatus under the conditions of a pressure of 6.5 GPa or higher and a temperature in the range of 1700 to 1900° C., then further heated up at a temperature of 2000° C. or higher: and a method in which the diamond-carbonate based sintered compact is produced from diamond powder and carbonate powder as material powders; the material powders are sintered in the HP/HT apparatus under the conditions of a pressure in the range of 6 to 12 GPa and a temperature in the range of 1700 to 2500° C.
Known references are: Japanese Patent Publication No. 2004-193522; Japanese Patent Publication No. H04-312982; Japanese Translation of PCT Publication No. 2006-502955; Japanese Patent Publication No. H05-194031; and
Japanese Patent No. 2,795,738.
The inherent characteristics of the diamond sintered compact have been utilized widely. For example, the aforementioned conventional art refers to a diamond-Co based sintered compact that has electrical conductivity, since the bonding phase in the diamond-Co based sintered compact consists of Co metal. So this diamond-Co based sintered compact has an advantage that the electrical discharge machining process is usable for machining this diamond-Co based sintered compact, but also has the disadvantage of low thermal resistance. On the other hand, the aforementioned conventional art refers to a diamond-carbonate based sintered compact that has the advantage of excellent thermal resistance; but due to its non-conductivity, the electrical discharge machining process is not usable for machining this diamond-carbonate based sintered compact. Therefore, there is a problem that only the laser beam machining process is usable for machining this diamond-carbonate based sintered compact. Hence, in conventional arts, it is very difficult to obtain a diamond sintered compact having both good electrical conductivity and other inherent characteristics of a diamond, such as hardness, thermal conductivity, thermal resistance and chemical stability. This is one of the limitations which prevent wide application of the diamond sintered compact.
The present invention relates to obtaining a diamond sintered compact, having both good conductivity and other characteristics of a natural diamond, such as, hardness, thermal conductivity, thermal resistance and chemical stability. The present invention also relates to a simplified and effective production method for the diamond sintered compact.